Helicobacter pylori CagA protein activates Akt and attenuates chemotherapeutics-induced apoptosis in gastric cancer cells

Molecular mechanisms underlying the action of carcinogens in gastric cancer with a glimpse into targeted therapy

BACKGROUND

Gastric cancer imposes a substantial global health burden despite its overall incidence decrease. A broad spectrum of inherited, environmental and infectious factors contributes to the development of gastric cancer. A profound understanding of the molecular underpinnings of gastric cancer has lagged compared to several other tumors with similar incidence and morbidity rates, owing to our limited knowledge of the role of carcinogens in this malignancy. The International Agency for Research on Cancer (IARC) has classified gastric carcinogenic agents into four groups based on scientific evidence from human and experimental animal studies. This review aims to explore the potential comprehensive molecular and biological impacts of carcinogens on gastric cancer development and their interactions and interferences with various cellular signaling pathways.

CONCLUSIONS

In this review, we highlight recent clinical trial data reported in the literature dealing with different ways to target various carcinogens in gastric cancer. Moreover, we touch upon other multidisciplinary therapeutic approaches such as surgery, adjuvant and neoadjuvant chemotherapy. Rational clinical trials focusing on identifying suitable patient populations are imperative to the success of single-agent therapeutics. Novel insights regarding signaling pathways that regulate gastric cancer can potentially improve treatment responses to targeted therapy alone or in combination with other/conventional treatments. Preventive strategies such as control of H. pylori infection through eradication or immunization as well as dietary habit and lifestyle changes may reduce the incidence of this multifactorial disease, especially in high prevalence areas. Further in-depth understanding of the molecular mechanisms involved in the role of carcinogenic agents in gastric cancer development may offer valuable information and update state-of-the-art resources for physicians and researchers to explore novel ways to combat this disease, from bench to bedside. A schematic outlining of the interaction between gastric carcinogenic agents and intracellular pathways in gastric cancer H. pylori stimulates multiple intracellular pathways, including PI3K/AKT, NF-κB, Wnt, Shh, Ras/Raf, c-MET, and JAK/STAT, leading to epithelial cell proliferation and differentiation, apoptosis, survival, motility, and inflammatory cytokine release. EBV can stimulate intracellular pathways such as the PI3K/Akt, RAS/RAF, JAK/STAT, Notch, TGF-β, and NF-κB, leading to cell survival and motility, proliferation, invasion, metastasis, and the transcription of anti-apoptotic genes and pro-inflammatory cytokines. Nicotine and alcohol can lead to angiogenesis, metastasis, survival, proliferation, pro-inflammatory, migration, and chemotactic by stimulating various intracellular signaling pathways such as PI3K/AKT, NF-κB, Ras/Raf, ROS, and JAK/STAT. Processed meat contains numerous carcinogenic compounds that affect multiple intracellular pathways such as sGC/cGMP, p38 MAPK, ERK, and PI3K/AKT, leading to anti-apoptosis, angiogenesis, metastasis, inflammatory responses, proliferation, and invasion. Lead compounds may interact with multiple signaling pathways such as PI3K/AKT, NF-κB, Ras/Raf, DNA methylation-dependent, and epigenetic-dependent, leading to tumorigenesis, carcinogenesis, malignancy, angiogenesis, DNA hypermethylation, cell survival, and cell proliferation. Stimulating signaling pathways such as PI3K/Akt, RAS/RAF, JAK/STAT, WNT, TGF-β, EGF, FGFR2, and E-cadherin through UV ionizing radiation leads to cell survival, proliferation, and immortalization in gastric cancer. The consequence of PI3K/AKT, NF-κB, Ras/Raf, ROS, JAK/STAT, and WNT signaling stimulation by the carcinogenic component of Pickled vegetables and salted fish is the Warburg effect, tumorigenesis, angiogenesis, proliferation, inflammatory response, and migration.

Bacterial-Viral Interactions in Human Orodigestive and Female Genital Tract Cancers: A Summary of Epidemiologic and Laboratory Evidence

Infectious agents, including viruses, bacteria, fungi, and parasites, have been linked to pathogenesis of human cancers, whereas viruses and bacteria account for more than 99% of infection associated cancers. The human microbiome consists of not only bacteria, but also viruses and fungi. The microbiome co-residing in specific anatomic niches may modulate oncologic potentials of infectious agents in carcinogenesis. In this review, we focused on interactions between viruses and bacteria for cancers arising from the orodigestive tract and the female genital tract. We examined the interactions of these two different biological entities in the context of human carcinogenesis in the following three fashions: (1) direct interactions, (2) indirect interactions, and (3) no interaction between the two groups, but both acting on the same host carcinogenic pathways, yielding synergistic or additive effects in human cancers, e.g., head and neck cancer, liver cancer, colon cancer, gastric cancer, and cervical cancer. We discuss the progress in the current literature and summarize the mechanisms of host-viral-bacterial interactions in various human cancers. Our goal was to evaluate existing evidence and identify gaps in the knowledge for future directions in infection and cancer.

Therapeutic effects, immunogenicity and cytotoxicity of a cell penetrating peptide-peptide nucleic acid conjugate against cagA of Helicobacter pylori in cell culture and animal model

BACKGROUND AND OBJECTIVES

Helicobacter pylori causes several gastrointestinal diseases, including asymptomatic gastritis, chronic peptic ulcer, duodenal ulcer, lymphoma of the mucosa-associated lymphoid tissue (MALT), and gastric adenocarcinoma. In recent years, failure to eradicate H. pylori infections has become an alarming problem for physicians. It is now clear that the current treatment strategies may become ineffective, necessitating the development of innovative antimicrobial compounds as alternative treatments.

MATERIALS AND METHODS

In this experimental study, a cell-penetrating peptide-conjugated peptide nucleic acid (CPP-PNA) was used to target the cagA expression. cagA expression was evaluated using RT-qPCR assay after treatment by the CPPPNA in cell culture and animal model. Additionally, immunogenicity and toxicity of the CPP-PNA were assessed in both cell culture and animal models.

RESULTS

Our analysis showed that cagA mRNA levels reduced in H. pylori-infected HT29 cells after treatment with CPPPNA in a dose-dependent manner. Also, cagA expression in bacterial RNA extracted from stomach tissue of mice treated with PNA was reduced compared to that of untreated mice. The expression of inflammatory cytokines also decreased in cells and tissue of H. pylori-infected mice after PNA treatment. The tested CPP-PNA showed no significant adverse effects on cell proliferation of cultured cells and no detectable toxicity and immunogenicity were observed in mice.

CONCLUSION

These results suggest the effectiveness of CPP-PNA in targeting CagA for various research and therapeutic purposes, offering a potential antisense therapy against H. pylori infections.

Metformin attenuates synergic effect of diabetes mellitus and Helicobacter pylori infection on gastric cancer cells proliferation by suppressing PTEN expression

It has been reported that CagA of Helicobacter pylori reduced PTEN expression by enhancing its promoter methylation. Furthermore, diabetes mellitus (DM) may also promote the methylation status of PTEN, a tumour suppressor gene in gastric cancer (GC). It is intriguing to explore whether DM may strengthen the tumorigenic effect of H pylori (HP) by promoting the methylation of PTEN promoter and whether the administration of metformin may reduce the risk of GC by suppressing the methylation of PTEN promoter. In this study, we enrolled 107 GC patients and grouped them as HP(-)DM(-) group, HP(+)DM(-) group and HP(+)DM(+) group. Bisulphite sequencing PCR evaluated methylation of PTEN promoter. Quantitative real-time PCR, immunohistochemistry and Western blot, immunofluorescence, flow cytometry and MTT assay were performed accordingly. DNA methylation of PTEN promoter was synergistically enhanced in HP(+)DM(+) patients, and the expression of PTEN was suppressed in HP(+)DM(+) patients. Cell apoptosis was decreased in HP(+)DM(+) group. Metformin showed an apparent effect on restoring CagA-induced elevation of PTEN promoter methylation, thus attenuating the PTEN expression. The reduced PTEN level led to increased proliferation and inhibited apoptosis of HGC-27 cells. In this study, we collected GC tumour tissues from GC patients with or without DM/HP to compare their PTEN methylation and expression while testing the effect of metformin on the methylation of PTEN promoter. In summary, our study suggested that DM could strengthen the tumorigenic effect of HP by promoting the PTEN promoter methylation, while metformin reduces GC risk by suppressing PTEN promoter methylation.

Helicobacter pylori CagA Protein Attenuates 5-Fu Sensitivity of Gastric Cancer Cells Through Upregulating Cellular Glucose Metabolism

Introduction

Gastric cancer (GC) is one of the most malignancies leading to human mortality due to its development, progress, metastasis and poor prognosis, despite the development of remarkable chemotherapy and surgery. The 5-fluorouracil (5-Fu) is an effective anti-gastric cancer agent. However, a fraction of GC patients acquire 5-Fu chemoresistance.

Methods

In this study, the CagA protein was detected from CagA-positive gastric cancer patients by qRT-PCR and immunohistochemistry. The 5-Fu resistant gastric cancer cell line was generated from MKN45-CagA cells which was transfected with CagA overexpression vector. Cellular glucose metabolism was determined by measurements of glucose uptake, lactate product and glycolysis enzymes.

Results

We report that the Helicobacter pylori (H. pylori)-secreted Cytotoxin-associated gene A (CagA) oncoprotein is positively correlated with 5-Fu resistance of gastric cancer. From totally 72 CagA-positive gastric cancer patients, CagA high-expressed patients showed more resistance to 5-Fu than CagA low-expressed patients. Moreover, statistical analysis revealed that CagA mRNA and protein expressions were significantly upregulated in 5-Fu resistant gastric cancer patients. We observed that CagA protein is upregulated in 5-Fu resistant gastric cancer cells compared with sensitive cells. Interestingly, cellular glucose metabolism was upregulated; the glucose uptake and lactate production were significantly higher in 5-Fu resistant gastric cancer cells. The Akt phosphorylation and expressions of glycolysis key enzymes, Hexokinase 2 and LDHA, were significantly upregulated in 5-Fu resistant gastric cancer cells. On the other way, inhibition of glycolysis or Akt pathway effectively overcame 5-Fu resistance from both in vitro and in vivo models. Finally, we report that the combination of Akt or glycolysis inhibitor with 5-Fu could synergistically enhance the cytotoxicity of 5-Fu to CagA-overexpressed gastric cancer cells.

Discussion

In summary, our study demonstrated a CagA-Akt-glycolysis-5-Fu resistance axis, contributing to the development of new therapeutic agents against chemoresistant human gastric cancer.

Helicobacter pylori-downregulated tumor necrosis factor receptor-associated protein 1 mediates apoptosis of human gastric epithelial cells

Heat shock proteins (HSPs) are crucial proteins in maintaining the homeostasis of human gastric epithelial cells. Tumor necrosis factor receptor-associated protein 1 (TRAP1), a member of the HSP90 family, has been shown to be involved in various crucial physiological processes, particularly against apoptosis. However, the regulation and function of TRAP1 in Helicobacter pylori infection is still unknown. Here, we found that TRAP1 expression was downregulated on human gastric epithelial cells during H. pylori infection by real-time polymerase chain reaction (PCR) and western blot analysis. Through virulence factors mutant H. pylori strains infection and inhibitors screening, we found that H. pylori vacuolating cytotoxin A ( vacA), but not cytotoxin-associated gene A ( cagA) protein, induced human gastric epithelial cells to downregulate TRAP1 via P38MAPK pathway by real-time PCR and western blot analysis. Furthermore, downregulation of TRAP1 with lentivirus carrying TRAP1 short hairpin RNA constructs impairs mitochondrial function, and increases apoptosis of gastric epithelial cells. The results indicate that H. pylori vacA downregulated TRAP1 is involved in the regulation of gastric epithelial cell apoptosis.

Value of CagA, HER2, ALDH1, and KiSS-1 in predicting metastasis and prognosis for gastric adenocarcinoma

BACKGROUND

Cytotoxin-associated gene A (CagA), is able to translocate into gastric epithelial cells. Human epidermal growth factor receptor 2 (also named as HER2, is a proto-oncogene which can encode a transmembrane receptor), Aldehyde dehydrogenase 1 (ALDH1, a biomarker of cancer stem cells), and KiSS-1 (a suppressor gene of cancer metastasis) are all valuably predictive biomarkers for various human cancers. The purpose of this study is to investigate the associations among CagA, HER2, ALDH1, and KiSS-1 in gastric adenocarcinoma (GAC), and their respective associations with clinical characteristics and survival in GAC.

METHODS

The expression of CagA, HER2, ALDH1, and KiSS-1 in 232 cases of whole GAC tissues were detected by immunohistochemical staining. Patient clinical and survival data were also collected.

RESULTS

Positive expression of CagA, HER2, and ALDH1 is significantly higher, and positive expression of KiSS-1 is significantly lower, in GAC tissues than in the corresponding normal tissues. Furthermore, the positive expression of CagA, HER2, ALDH1, and KiSS-1 were significantly associated with tumor grade, tumor stage, lymph node metastasis (LNM) stage, and tumor node metastasis (TNM) stages, and with patients' overall survival (OS); whereas the KiSS-1 positive group had longer OS than did the KiSS-1 negative group. In logistic analysis, positive expression of CagA, HER2, ALDH1, and KiSS-1 are significantly associated with LNM of patients with GAC. COX regression analysis indicated that positive expression of CagA, HER2, ALDH1, and KiSS-1, and tumor stages, LNM stages, and TNM stages were independent prognostic factors for patients with GAC.

CONCLUSIONS

Expression of CagA, HER2, ALDH1, and KiSS-1 should be considered as promising biomarkers for metastasis and prognosis, as well as potential therapeutic targets for GAC.